HVDC Inter-Island

The North Island HVDC terminal station at Haywards near Wellington, showing the Pole 2 converter building and switchyards
Country	New Zealand
General direction	South-North
From	Benmore Hydroelectric Power Station, near Otematata, Canterbury
To	Haywards transmission substation, Lower Hutt
Owner	Transpower New Zealand Limited
Operator	Transpower New Zealand Limited
Manufacturer of substations	ABB Group / Siemens
Construction started	1961
Commissioned	April 1965
Type	Bipole HVDC scheme with overhead transmission line and Submarine power cables across the Cook Strait
Type of current	HVDC
Total length	610 km (380 mi)
Power rating	1200 MW
AC Voltage	220 kV
DC Voltage	±350 kV
No. of poles	Two

The HVDC Inter-Island link is a 610 km (380 mi) long, 1200 MW bipolar high-voltage direct current (HVDC) transmission system connecting the electricity networks of the North and South Islands of New Zealand together. It is commonly referred to as the Cook Strait cable, which is somewhat of a misnomer, because only a short section of the complete link is in cable, and there are actually three operational HVDC power cables across Cook Strait. However, the term Cook Strait cable is commonly used in the media and press releases. The link is owned and operated by state-owned transmission company Transpower New Zealand.

The link starts at the Benmore Hydroelectric Power Station, on the Waitaki River in Canterbury, and travels 534 kilometres (332 mi) on an overhead transmission line through inland Canterbury and Marlborough to Fighting Bay in the Marlborough Sounds. From Fighting Bay, the link travels 40 km via submarine cables across Cook Strait to Oteranga Bay, near Wellington, before travelling the final 37 km on overhead lines to Haywards transmission substation in Lower Hutt.

The HVDC link was first commissioned in April 1965 to primarily transport electricity from the generation-rich South Island to the more populous North Island. The link originally was a bipolar 600 MW link with mercury arc valves, until the original equipment was paralleled onto a single pole (Pole 1) in 1992, and a new thyristor-based pole (Pole 2) was commissioned alongside it, increasing the link capacity to 1040 MW. Pole 1 was fully decommissioned effective 1 August 2012, and the replacement thyristor-based Pole 3 was fully commissioned on 29 May 2013, restoring the link to a bipolar 1200 MW configuration .

The HVDC Inter Island link starts at two converter stations located adjacent to Benmore Hydroelectric Power Station in the Waitaki Valley. Electricity is taken from the main Benmore switchyard, which interconnects the Benmore generators and rest of the South Island transmission grid, at 220 kV via tie-lines across the Benmore tailrace. The AC power is converted at the stations to ±350 kV HVDC for transmission to the North Island.